1. Field of the Invention
The present invention relates to an optical disc reproduction apparatus for an optical disc including a track having a plurality of sectors.
2. Description of the Related Art
FIG. 15 is a black diagram illustrating a structure of a conventional optical disc reproduction apparatus 1100.
The optical disc reproduction apparatus 1100 includes an address section detection section 1106, a wobble detection section 1107, a wobble PLL circuit 1105, a data PLL circuit 1112, a gate signal generation section 1113, a defect and unrecorded portion detection section 1115, an unrecorded sector determination section 1118, and a system controller 1117.
In this specification, the term “unrecorded portion” refers to a portion in an optical disc in which no data has been recorded.
The defect and unrecorded portion detection section 1115 determines whether a defect in a sector is currently being reproduced or not, and generates a defect detection signal representing a defect in the sector.
The defect and unrecorded portion detection section 1115 also determines whether an unrecorded portion of a sector is being reproduced or not, and generates an unrecorded portion detection signal representing an unrecorded sector.
FIG. 16 shows a structure of the unrecorded sector determination section 1118.
The unrecorded sector determination section 1118 includes an unrecorded portion time measuring section 2402 and a comparator 2405.
The unrecorded portion detection signal which is output from the defect and unrecorded portion detection section 1115 is input to the unrecorded portion time measuring section 2402.
The unrecorded portion time measuring section 2402 measures a reproduction time of the unrecorded portion of the sector, and outputs unrecorded portion time data which represents the measured reproduction time of the unrecorded portion of the sector.
In the comparator 2405, a reference level (unrecorded sector detection level) is preset. The comparator 2405 compares the unrecorded portion time data which is output from the unrecorded portion time measuring section 2402 with the reference level, and outputs an unrecorded sector determination signal which determines whether the sector is an unrecorded sector or not.
As described above, the optical disc reproduction apparatus 1100 determines whether the sector is an unrecorded sector or not based only on the unrecorded portion time data.
FIG. 17 shows a structure of the wobble PLL circuit 1108.
The wobble PLL circuit 1108 includes a phase comparator 1501, a switch 1502, a phase compensator 1503, a variable oscillator 1504, and a frequency divider 1505.
The phase comparator 1501 compares the phase of a wobble clock signal which has been frequency-divided by the frequency divider 1505 with the phase of a wobble signal. The phase comparator 1501 then outputs a signal representing the comparison result to the variable oscillator 1504 via the switch 1502 and the phase compensator 1503, such that the wobble clock signal is synchronized to the wobble signal.
The wobble PLL circuit 1108 (FIG. 15) receives an address section detection signal which is output from the address section detection section 1106. The address section detection signal turns the switch 1502 off, and thus the wobble PLL circuit 1108 is put on hold while the address section is being detected.
When the address section detection signal cannot be detected a prescribed number of times the system controller 1117 (FIG. 15) determines that the frequency of a data read clock signal output by the data PLL circuit 1112 is abnormal.
Thus, the optical disc reproduction apparatus 1100 makes a determination on the abnormality of the frequency of the data read clock signal based on the address section detection signal.
When an optical disc which is marketed without any data recorded in a particular data section is attempted to be reproduced and a request for reproducing an unrecorded sector is issued, it should be detected that the sector which is now being reproduced is an unrecorded sector in order to stably perform the reproduction operation.
As described above, the conventional optical disc reproduction apparatus 1100 determines whether the sector which is currently being reproduced is an unrecorded sector or not based only on the unrecorded portion time data. This system has the following problems. In the case where the reproduction speed of information recorded in a sector which is in an inner area of the optical disc is different from the reproduction speed of information recorded in a sector which is in an outer area of the optical disc (for example, in CAV reproduction), it cannot be determined whether the sector which is currently being reproduced is an unrecorded sector or not. The reason is because the unrecorded portion time relies on the reproduction speed of information.
In the case of CLV reproductions CLV control may not be accurately performed immediately after a seek operation, resulting in the reproduction speed of information varying sector by sector. In this case also, it cannot be determined whether the sector which is currently being reproduced is an unrecorded sector or not. The reason is, again, because the unrecorded portion time relies on the reproduction speed of information.
As described above, the conventional optical disc reproduction apparatus 1100 puts the wobble PLL circuit on hold only for a term during which an address section of the sector is being detected. This system has the problem that the address section cannot be accurately detected based on a wobble clock signal. The reason is that a prescribed term, during which the address is not detected, includes a term during which the wobble clock signal is disturbed. The disturbance of the wobble clock signal is caused because the address section cannot be accurately detected.
The conventional optical disc reproduction apparatus 1100 detects a frequency abnormality of the data read clock signal based only on the address section detection signal. According to such a system, the number of times when an address section detection signal is not detected needs to be counted. Therefore, the frequency abnormality of the data read clock signal cannot be detected at a high speed.
FIG. 18 explains how the wobble clock signal is disturbed. (a) shows the waveform of the address section detection signal, and (b) shows the waveform of the wobble signal.
In general, when the optical disc reproduction apparatus 1100 (FIG. 15) is operated, the timing at which the address section detection section 1106 detects the address section is delayed. As a result, the wobble PLL circuit 1108 operates for a term 2001, which disturbs the wobble clock signal. Due to a delay in response of the band pass filter of the wobble PLL circuit 1108, the wobble signal is disturbed for a term 2002. This causes the wobble clock signal to be disturbed.